Disruptive behavior disorders (DBDs;conduct disorder and oppositional-defiant disorder) with severe aggression constitute a public health problem for which evidence-based treatment options are limited. Increasing numbers of youth with aggression are being treated with atypical antipsychotics without good evidence of safety or incremental advantage over safer stimulants. This double-blind, placebo-controlled, parallel groups study will compare the effectiveness of (a) parent training in behavior management (PMT) + placebo (PBO), (b) PMT + d-methylphenidate (d-MPH), and (c) PMT + d-MPH + risperidone (RIS) in children with severe aggression, primary DBDs, and comorbid ADHD. Participants must exhibit a clear history and current pattern of serious physical aggression (i.e., moderate or higher scores on the Modified Overt Aggression Scale (OAS-M), a Clinical Global Impressions (CGI) Scale Severity score of 4 or higher for aggression), and high scores on the on the Disruptive-Total of the Nisonger Child Behavior Rating Form (NCBRF) . The primary aims are to determine (a) if PMT + d-MPH are superior to PMT+ PBO and (b) if PMT + d-MPH + RIS are superior to PMT + d-MPH and to PMT + PBO. Secondary aims include determining whether type of aggression (reactive vs. proactive) moderates treatment response. Design: Two hundred sixteen children across 4 sites (Case Western Reserve, Ohio State, Pittsburgh, &Stony Brook) will be randomized to 9 weeks double-blind of PMT + PBO (n=72), PMT + MPH (n=72), or PMT + MPH + RIS (n=72). All groups will receive a 12-session course of carefully monitored, empirically-based PMT. Responders will be followed on their assigned treatments in a 12-week Extension, and all participants will be assessed at one year after baseline. Clinical change will be measured by (a) parent ratings on the NCBRF &ADHD Symptom Checklist (CL);(b) teacher ratings on the ADHD Symptom CL;(c) clinician interview of the child with OAS-M;(d) clinician CGI-Improvement score (CGI-I);and direct observations of child-parent behavior. The primary outcome measure is the NCBRF Disruptive Total score;secondary outcomes are CGI-I, response rate (NCBRF reduction of at least 25%, plus CGI-I score of 1 or 2), other NCBRF and ADHD Symptom Checklist subscales, and cognitive tests. Baseline score on the Antisocial Behavior Scale will assess type of aggression (reactive or proactive) as a potential moderator. AEs and tolerability will also be assessed. This study will assess the use of placebo, d-methylphenidate (Focalin), and d-methylphenidate plus risperidone (an atypical antipsychotic drug;brand name Risperdal) against the back-drop of behavior therapy which will be taught to the parents of participants. The participants will be children ages 6 to 12 years, inclusive, who have been diagnosed with a disruptive behavior disorder plus ADHD and who display significant aggressive behavior. Given the increasing rates and severity of violence in our society, this investigation will help to determine if drug therapy, combined with parent-provided behavior therapy, can reduce child aggression.